Utilization of a suction nozzle and jet nozzle for cleaning moving objects

ABSTRACT

Cleaning apparatus, and a method of utilization of the apparatus, cleans an object with a moving surface, such as a roll. The cleaning apparatus includes a nozzle head with a suction nozzle and a jet nozzle for emitting a liquid jet towards the roll. A sub-pressure is maintained in a chamber of the suction nozzle in order to evacuate liquid and released impurities with the aid of air flowing through a gap between the roll and the orifice edge. The jet nozzle is spaced from the inside of the suction nozzle and at the center of the suction nozzle to form a circumferential passage, the passage communicating with an evacuation pipe. The nozzle head also includes a structure to supply compressed air into the chamber through the gap in order to encounter and carry with it toward the passage liquid and impurities, cooperating with the suction effect maintained in the chamber and the evacuation pipe. The compressed air also has the advantage of drying the roll treated with liquid.

The present invention relates to apparatus for cleaning the surfaces ofobjects in movement, comprising at least one nozzle head including ahousing forming an elongate suction nozzle that terminates in an orificeedge surrounding an opening, which suction nozzle contains a chamberincluding said opening, the suction nozzle being arranged spaced fromsaid surface to form a circumferential gap between the surface and theorifice edge of the suction nozzle, the nozzle head also including atleast one jet nozzle arranged in said chamber spaced from said openingin order to emit a jet of a treating liquid to produce a predeterminedtreatment area on said surface; pipe means including an evacuation pipeconnected to the chamber of the suction nozzle, a supply pipe connectedto the jet nozzle to supply treating liquid under pressure, and a vacuumsource arranged to maintain a subpressure in the chamber so as, with theaid of air flowing in through said gap, to evacuate liquid and materialreleased from the surface; and an actuator to move the nozzle headsubstantially perpendicularly to the direction of movement of theobject, said nozzle head being arranged to be guided along the movingsurface at a constant distance therefrom in order to maintain said gap.

The function of a roll rotating in contact with a material web isgradually deteriorated by material collecting on the shell surface ofthe roll. The degree of deterioration of the roll function varies fromone area to another as well as the type of material and quantity thereofthat collects. An example of such rolls is cliche rolls where printingink adheres to the shell surface and collects so that the quality of thepattern to be transferred to the material web passing it isdeteriorated. Also contributing to this deterioration is the fact thatdirt and fibres collect in the ink layer and that this ink layer may beuneven both peripherally and in axial direction, the deteriorationtherefore appearing unevenly. One alternative for restoring the functionof the roll has been to stop production in order to clean the shellsurface by various means. Since falls in the production are notdesirable, another alternative has been to use stationary aids such asbrushes and scrapers to try to clean the shell surface during operation.Both alternatives are time consuming and troublesome to perform becausethe space around the roll is usually rather cramped. The latteralternative also means that brushes and scrapers become worn and theircleaning effect is in time reduced and they must be replaced at regularintervals. Material is collected in the brushes and they must also becleaned. If scrapers are used they will wipe over some of the materialwhen larger quantities have built up on the shell surface, and thismaterial then remains. Cleaning in accordance with the first alternativemust then be performed and continuous operation is impossible.

JP-63-004949 describes apparatus of the type defined in the preamble tothe claims, but the moving surface is treated with an air jet and thusdoes not deal with the problems associated with the use of liquid astreating agent. Furthermore, air as treating agent is quite insufficientto achieve efficient and complete cleaning of the object. The air jet isnot strong enough to break up hard layers of impurities on a movingsurface and there is a risk of dust and other impurities being pressedout through the air gaps in the suction nozzle. The nozzle for the airjet is also mounted in the wall of the suction nozzle and the latter isasymmetrical in shape to extend obliquely into the chamber, so that theflow of air and impurities becomes uneven and difficult to control,particularly axially and radially inside the air gap. U.S. Pat. No.3,737,940 describes a device based on mechanical cleaning with the aidof a rotating brush or soft roller journalled in a housing that extendslongitudinally in the axial direction of the roll. The surface of theroll is sprayed with liquid, i.e. under negligible pressure, both beforeand after the brush. Such a device is complicated in design as well asbeing relatively large and clumsy. The most important drawback, however,is that its cleaning capacity is insufficient and it has little or noeffect on hard layers of impurities.

The object of the present invention is to provide an improved apparatuswhich will enable the moving surface of a duty object to be cleanedwhile still in continuous operation, i.e. without the object having tobe stopped and possibly removed and replaced for reconditioning for itsspecific function, and which is so efficient that even hard layers ofimpurities can be removed from the object, and which also leaves a drymoving surface although liquid is used as treating agent.

The apparatus according to the invention is characterized substantiallyin that the jet nozzle is arranged at a distance from the inside of thesuction nozzle and at or close to the centre of the suction nozzle toform a free circumferential passage of the chamber between the insideand the jet nozzle, said passage communicating with said evacuationpipe, and that the nozzle head includes means for supplying compressedair into the chamber via said gap in order to encounter and carry withit treatment liquid deflected from the surface and material releasedfrom the surface in the direction to and through said passage incooperation with the suction effect maintained in the chamber andevacuation pipe.

The invention will be described in more detail in the following withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a lateral view of a cleaning unit of the apparatus accordingthe invention, with a nozzle head displaced from the centre of a patternroll.

FIG. 2 is an end view of the cleaning unit according to FIG. 1.

FIG. 3 is a service unit of the apparatus according to the invention,for serving the cleaning unit according to FIG. 1.

FIG. 4 is a perspective view of a nozzle head substantially similar tothat in FIG. 1, but directed towards the centre of a pattern roll to bereconditioned.

FIG. 5 is an end view of the nozzle head and pattern roll according toFIG. 4.

FIG. 6 is a perspective view of a nozzle head arranged to clean a flatsection of an object running over at least two rolls.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1 and 2 it is shown therein schematically acleaning unit 1 of an apparatus according to the invention for cleaninga surface 2 in movement, whereas FIG. 3 shows schematically a serviceunit 3 of the apparatus to serve the cleaning unit 1. The cleaning unit1 comprises a nozzle head 4 connected to the service unit via pipe means5. In the embodiment shown the moving surface 2 to be cleaned consistsof the shell surface of a rotating pattern roll 6 which forms a nip witha counter roll 7, a paper web 8 passing through the nip where printingis effected on the side in contact with the pattern roll 6. Ink issupplied to the pattern roll 6 by an inking feed roller 9, the shellsurface of which passes through an ink solution in a trough 10.

The pipe means 5 comprise a supply pipe 11 for fresh treating liquid,e.g. water or some other solvent, and an evacuation pipe 12 for spentliquid which now contains impurities, i.e. ink and loose fibres from thepaper web in the case described, as well as dirt and dust. Theevacuation pipe 12 is provided with an intermediate portion 13 which isflexible, and end portions 14, 15 at the two units 1, 3, which are rigidand bent in suitable manner. The supply pipe 11 for fresh treatingliquid extends inside the evacuation pipe 12 and may consist of a hose.

The service unit 3 includes a tank 16 containing fresh treating liquidin one or more containers, and equipment for cleaning used liquidcontaining impurities. Above the tank 16 is a vacuum pump 17 to whichthe evacuation pipe 12 is connected by its end portion 15, the vacuumpump 17 being connected to said cleaning equipment in the tank 16 bymeans of a return pipe 18. An air filter 19 is connected to the cleaningequipment to let out air separated from the liquid containing impuritiesand supplied at the cleaning unit 1 to serve as carrier for the liquidused and impurities released. A high-pressure pump 20 arranged above thetank 16 is connected to the clean treating liquid in the tank 16. Thehose 11 is connected to the high-pressure pump 20 which is thus arrangedto feed clean treating liquid to the nozzle head 4 via the hose 11.

The nozzle head 4 can be moved parallel to the shaft of the pattern roll6 in a to and fro movement effected by an actuator 21 in the form of apneumatic or hydraulic cylinder rigidly mounted on a stand 22 (not shownin FIG. 2). The plunger in the cylinder 21 is rigidly connected to thebent, rigid end portion 14 of the evacuation pipe 12 via a connectionpiece 23. The nozzle head 4 is rigidly connected to the end portion 14so that the nozzle head 4 is guided along the shell surface 2 at aconstant distance therefrom to ensure a gap 34, as will be explainedfurther below. In the embodiment according to FIGS. 1 and 2 the centreline of the nozzle head 4 is somewhat displaced from the centre of thepattern roll 6, whereas the nozzle head 4 in the embodiment according toFIGS. 4 and 5 is directed exactly towards the centre.

The nozzle head 4 (see FIGS. 4 and 5) includes a housing 25 consistingof a casing with circular cross section, and a jet nozzle 24 arranged inthe casing 25 in the immediate vicinity of the centre line of thecasing. The casing 25, which is preferably cylindrical, itself forms anelongate suction nozzle 26 which terminates in an orifice edge 29surrounding an opening 39 free from mechanical parts. The suction nozzle26 contains a chamber 32 comprising said opening 39 and is arrangedspaced from the shell surface 2 to form a circumferential gap 34 betweenthe shell surface 22 and orifice edge 29. The jet nozzle 24 is arrangedin the chamber 32 of the casing, spaced axially from the opening 39, toemit a jet 40 of treating liquid producing a predetermined treatmentarea 41 on the shell surface 2. A holder 27 is mounted inside the casing25, the location of which may be fixed but is preferably adjustable todifferent positions with the aid of a suitable adjustment means (notshown). The holder 27 carries the jet nozzle 24, the orifice 28 of whichis located centrally in the casing 25. The position of the jet nozzle 24in relation to the holder 27 may be fixed or adjustable. The hose 11 isconnected to a central, axial aperture 30 in the holder 27, thisaperture 30 communicating with the jet nozzle 24. The holder 27 is alsoprovided with a plurality of peripheral, axial through-holes 31 throughwhich the evacuation pipe 12 communicates openly with the chamber 32 ofthe suction nozzle 26. The front end of the suction nozzle 26 is shapedwith a contour to fit the curvature of the pattern roll 6 to producesaid gap 34. This contour thus varies in shape depending on thealignment of the suction nozzle 26 in relation to the centre of thepattern roll, as illustrated by the two embodiments in FIG. 2 and FIG.5.

During linear displacement of the nozzle head 4 this is guided by itssuspension in the cylinder 21 so that the size of the gap 34 is keptconstant all the time.

According to the present invention the jet nozzle 24 is arranged spacedfrom the cylindrical inner side 42 of the suction nozzle 26 so that afree, circumferential passage 43 of the chamber 32 is formed between theinner side 42 and the jet nozzle 24. This passage 43 thus communicatesdirectly with the evacuation pipe 12 via the axial apertures 31 in theholder 27.

According to the present invention the nozzle head 4 also includes means44 for a controlled supply of compressed air to the chamber 32 via saidgap 34 in order to encounter and carry with it liquid deflected from thesurface 2 and material released from the shell surface 2 towards andthrough said passage 43. The supply means 44 for compressed air includesa pipe 35 and a distributor connected to the pipe 35 for forced supplyof compressed air to the suction nozzle 26 close to the orifice edge 29so that a strong flow of air is introduced into the chamber 32 throughthe gap 34. The increased air flow also results in favourable drying ofthe shell surface 2. The compressed air may be supplied all around thegap 34 or only to certain parts of it, particularly downstream of theorifice edge 29 in that case when the pattern roll 6 or other object isrotating with such high speed that its surface 2 carries with it a layerof air into the chamber 32 through the gap 34 upstream of the orificeedge 29, seen in the direction of rotation of the pattern roll. Thecompressed air jets are thus aligned so that they hit the shell surface2 upon passage through the gap 34. A suitable alignment is thus about40°-90° in relation to the outer surface of the casing 25. Thedistributor is not shown in FIG. 4 but is generally intimated by arrows33 to illustrate the distribution of the compressed air downstream ofthe orifice edge 29. In FIG. 5 the distributor is shown in the form ofan endless pipe 37 extending around the entire suction nozzle 26, closeto the orifice edge 29, and provided with a plurality of apertures 38facing towards the gap 34 so that jets 45 of compressed air are forcedinto the chamber 32 via the gap 34 at the same time as hitting the shellsurface 2 to dry it.

FIG. 6 shows a nozzle head 4 similar to that in FIG. 4 but modified totreat the flat surface 2 of a moving wire or felt 36 in a paper machinein operation. The only difference is that the orifice edge 29 of thecasing 25 has been made flat instead of concave so that the orifice edge29 lies in a plane perpendicular to the central axis of the nozzle head4. A nozzle head of the type shown in FIG. 4, i.e. with an inwardlycurving orifice edge 29, can also be used to great advantage forcleaning a wire or felt 36 by being mounted next to a curved surface ofthe wire or felt, i.e. where it runs over a roll. A greatly improvedresult is obtained since the wire or felt exposes inner portions as itpasses and is bent around a roll and the liquid jet 40 also acts onthese inner portions of the surface 2.

The term "impurities" refers to all material that, particularly duringoperation, adheres to the surface 2 of the object 6 and includes notonly particles such as dust and dirt from the surroundings and fibresfrom the material web, e.g. paper web, in contact with the movingsurface, but also such material which, with the aid of the movingsurface, is to be applied on a passing web of material, or which isalready on the web of material.

The liquid used for cleaning the surface 2 of the object 6 may be anysuitable liquid whatsoever, depending on the nature of the movingsurface to be cleaned. The liquid may be at ambient temperature orincreased temperature. It is totally free from solid particles sincethese might damage the surface 2 of the object 6. In most cases it issufficient to use fresh water.

The apparatus also includes a control unit (not shown) which influencesthe actuator 21 and controls the movements of the nozzle head 4 to andfro in relation to the velocity of the roll, wire, felt or other object6 so that the entire surface 2 is treated and cleaned within a certainperiod of time. The rate of feed of the nozzle head 4 across thedirection of movement of the object is selected in proportion to theeffective dimension of the treatment area 41 (transversely over theobject 6). If the latter is for instance 10 mm, the feed rate may be atmost 8 mm per revolution. With the aid of a step motor, for instance, orsome other suitable actuator, the control unit can be programmed tocontrol the nozzle head 4 to clean only, or more frequently, specificparts of a roll, for instance.

If desired the apparatus may be provided with one or more additionalnozzle heads 4 in order to increase its capacity.

The shape of the treatment area 41, determined by the shape of theopening 28, may be oblong with little width, which is preferred, or ovalor circular. The largest effective dimension of the treatment area 41 isgenerally perpendicular to the direction of movement of the object 6 andis suitably 1-50 mm, preferably 5-10 mm, depending on prevailingoperating conditions. The diverging shape of the jet 40 then encompassesan angle of about 5°-50°. The larger the angle the greater must be theshortest distance of the treatment area 41 to the gap 34. If the angleis 45°, therefore, this distance is at least about 15-20 mm.

The treating liquid supplied to the jet nozzle 24 has a pressure of50-500 bar, preferably 150-300 bar, depending on the prevailingoperating conditions. The liquid jet 40 thus hits the object 6 at a veryhigh pressure and the liquid jet 40 thus has a mechanical effect in thatit breaks up impurities on the object and knocks them loose, thereaftertaking the impurities with it. At the same time the surface of theobject is washed with treating liquid when the jet 40 hits the surface,and at least some of the impurities may dissolve immediately in theliquid or during evacuation.

The quantity of liquid used is suitably 0.12-5 l/min, preferably 0.5-1.5l/min, for each nozzle head 4, depending on the prevailing operatingconditions.

The size of the gap 34, i.e. the distance between the orifice edge 29and the surface 2 of the object 6 is suitably 1-5 mm, preferably 1.5-3.0mm, depending on the prevailing operating conditions.

The distance of the jet nozzle 24 to the surface 2 of the object 6 issuitably 2-20 mm, preferably 2-5 mm, depending on the prevailingoperating conditions. However, it should never be less than the size ofthe gap 34 in any operating case.

The limit of the treatment area 41 produced by the liquid jet 40 islocated at a distance from the gap 34 to prevent liquid and impuritiessquirting out through the gap 34 and also to enable compressed air to beforced in through the gap 34 so that a flow of air will entirelysurround the liquid jet 40 and be deflected up towards and through thepassage 43 to serve as transport air for the used deflected liquid andimpurities. Said distance is at least 10 mm.

In order to ensure a uniform flow of liquid, air and impurities past thejet nozzle 24, as well as an efficient flow of air away from the gap 34into the chamber 32, it is also important for the jet nozzle 24 to bearranged in or close to the centre of the casing 25. The jet nozzle 24or just its orifice 28 can be adjusted so that the liquid jet 40 formsan angle of 0°-45° with the centre line of the casing 25, the liquid jet40 thus forming an angle of less than 90° with the tangent at the pointwhere the liquid jet impacts the roll, seen against the direction ofrotation. Depending on the alignment of the jet nozzle 24, the centre ofthe treatment area 41 can be moved from 0 to 20 mm towards the upstreampart of the gap 34 in order to compensate for the speed of rotation ofthe roll.

It will be understood that in the evacuation pipe 12 and associatedchamber 32 the subpressure is regulated to a level at which thenecessary suction force is created in order to evacuate all liquid, airand impurities backwards from the suction nozzle 26 and through theevacuation pipe 12 without any liquid, air or impurities penetrating outthrough the gap 34.

Thus, the invention provides an efficient apparatus for cleaningrotating rolls and wires, for instance, without the aid of mechanicalconstruction elements working on the surface. The invention enablesrolls to be cleaned with liquid jets at extremely high pressure whilestill obtaining a dry surface. The apparatus thus provides a combinedcleaning and drying effect.

I claim:
 1. Apparatus for cleaning a surface of an object moving in afirst direction, said apparatus comprising:at least one nozzle head,comprising a housing forming an elongated suction nozzle, including acenter, that terminates at a first end thereof in an orifice edge, whichorifice edge surrounds and defines an opening; a chamber including saidopening; and at least one jet nozzle disposed in said chamber spacedfrom said opening and capable of emitting a jet of treatment liquid;said nozzle head positioned with respect to the surface of an object tobe cleaned so that a circumferential gap is formed between the surfaceto be cleaned and said orifice edge, and so that said jet of treatmentliquid impacts a treatment area of the surface to be cleaned; anevacuation pipe connected to said chamber of said suction nozzle; asupply pipe connected to said jet nozzle for supplying treatment liquidunder superatmospheric pressure thereto; a vacuum source connected tosaid chamber by said evacuation pipe for maintaining a sub-pressure insaid chamber so that said vacuum source, along with air flowing throughthe gap between said nozzle head and the surface to be cleaned,evacuates liquid and material released from the surface from saidchamber; an actuator for moving said nozzle head in a second directionsubstantially perpendicular to the first direction, said nozzle headguided during movement by said actuator so as to maintain the gapbetween said nozzle head and the surface to be cleaned; said jet nozzledisposed within said suction nozzle at a position at or near the centerof said suction nozzle to define an open circumferential passage betweenan interior wall portion of said jet nozzle and said suction nozzle,said open circumferential passage connected to said evacuation pipe; andmeans for supplying compressed air into said suction nozzle chamberthrough the gap between said nozzle head and the surface of the objectto be cleaned so that the compressed air encounters and carries with ittreatment liquid deflected from the surface of the object to be cleaned,and material released from the surface of the object to be cleaned, intoand through said open circumferential passage and under the influence ofsaid vacuum source.
 2. Apparatus as recited in claim 1 wherein saidsuction nozzle has a circular cross-section.
 3. Apparatus as recited inclaim 1 wherein said means for supplying compressed air is mounted in aposition in which it supplies compressed air into said suction nozzlechamber only at that part of the gap defined between said nozzle headand the surface of the object to be cleaned located downstream, in thefirst direction of said nozzle head, in the gap.
 4. Apparatus as recitedin claim 1 further comprising a service unit, said service unitcomprising said vacuum source, a tank for storing cleaning liquid, ahigh pressure pump connected to said supply pipe and said tank, andconnected to said evacuation pipe means for receiving polluted liquidfrom said evacuation pipe and separating impurities and transport airfrom the polluted liquid.
 5. Apparatus as recited in claim 1 whereinsaid housing comprises a tubular casing; and further comprising a holderdisposed within said tubular casing centrally mounting said jet nozzletherein, a plurality of peripheral, axial, through-extending openingsbeing provided in said holder surrounding said jet nozzle and definingsaid open circumferential passage.
 6. Apparatus as recited in claim 5wherein a position of said holder within said tubular casing isadjustable to thereby allow adjustment of the position of said jetnozzle with respect to said orifice edge.
 7. Apparatus as recited inclaim 1 wherein said means for supplying compressed air comprises adistributor extending around at least a portion of said orifice edge,and having a plurality of openings facing the gap between said nozzlehead and the object to be cleaned.
 8. Apparatus as recited in claim 7wherein said distributor comprises a pipe.
 9. Apparatus as recited inclaim 1 wherein said jet nozzle emits a diverging liquid streamencompassing an angle of 5°-50°.
 10. Apparatus as recited in claim 1further comprising a control unit for controlling said actuator inresponse to a velocity and size of the surface to be cleaned to insureeffective cleaning after a predetermined period of time.
 11. Acombination comprising:an object having a surface to be cleaned, saidsurface moving in a first direction; and a cleaning apparatus forcleaning said surface, said cleaning apparatus comprising: at least onenozzle head, comprising a housing forming an elongated suction nozzlethat terminates at a first end thereof in an orifice edge, which orificeedge surrounds and defines an opening a center, and a chamber includingsaid opening, and at least one jet nozzle disposed in said chamberspaced from said opening and capable of emitting a jet of treatmentliquid; said nozzle head positioned with respect to said surface so thata circumferential gap is formed between said surface and said orificeedge, and so that said jet of treatment liquid impacts a treatment areaof said surface; an evacuation pipe connected to said chamber of saidsuction nozzle; a supply pipe connected to said jet nozzle for supplyingtreatment liquid under superatmospheric pressure thereto; a vacuumsource connected to said chamber by said evacuation pipe for maintaininga sub-pressure in said chamber so that said vacuum source, along withair flowing through the gap between said nozzle head and said surface,evacuates liquid and material released from said surface from saidchamber; an actuator for moving said nozzle head in a second directionsubstantially perpendicular to the first direction, said nozzle headguided during movement by said actuator so as to maintain said gap; saidjet nozzle disposed within said suction nozzle at a position at or nearthe center of said suction nozzle to define an open circumferentialpassage between an interior wall portion of said suction nozzle and saidjet nozzle, said open circumferential passage connected to saidevacuation pipe; and means for supplying compressed air into saidsuction nozzle chamber through said gap so that the compressed airencounters and carries with it treatment liquid deflected from saidsurface, and material released from said surface, into and through saidopen circumferential passage and under influence of said vacuum source.12. A combination as recited in claim 11 wherein said gap has a size;and wherein said nozzle head is positioned with respect to said surfaceso that the size of said gap is between 1-5 mm.
 13. A combination asrecited in claim 12 wherein said gap has a size; and wherein there is adistance between said jet nozzle and said surface; and wherein thedistance between said jet nozzle and said surface is between 2-20 mm,and greater than the size of said gap.
 14. A combination as recited inclaim 13 wherein there is a treatment area of said liquid jet from saidjet nozzle on said surface, which treatment area is spaced from said gapless than 10 mm.
 15. A combination as recited in claim 11 wherein saidgap has a size; and wherein said nozzle head is positioned with respectto said surface so that the size of said gap is between 1.5-3 mm.
 16. Amethod of cleaning a surface, using a nozzle head including a suctionnozzle terminating at a first end thereof in an orifice edge whichsurrounds and defines an opening, a chamber including the opening, and ajet nozzle for emitting a jet of treatment liquid, said methodcomprising the steps of:(a) positioning the nozzle head with respect tothe surface so that a circumferential gap is formed between the surfaceand the orifice edge and so that a liquid jet from the jet nozzleimpacts a treatment area of the surface; (b) moving the surface in afirst direction; (c) as the surface is moving simultaneously: (c1)supplying cleaning liquid to the jet nozzle and directing the cleaningliquid with the jet nozzle onto the surface predetermined area; (c2)applying a suction force to the chamber to withdraw gas, liquid, andentrained material, away from the surface through the chamber; and (c3)supplying compressed air to the gap to encounter and carry with ittreatment liquid and material cleaned off the surface; and (d) movingthe nozzle head in a second direction substantially perpendicular to thefirst direction while practicing steps (c1)-(c3).
 17. A method asrecited in claim 16 wherein step (c1) is practiced so as to directliquid at a pressure of between about 150-300 bar from the jet nozzle.18. A method as recited in claim 17 wherein step (c1) is practiced so asto emit treatment liquid from the jet nozzle at a rate of between about0.5-1.5 liters per minute.
 19. A method as recited in claim 18 whereinstep (a) is practiced so that the gap has a size that is between about1.5-3 mm, and so that the jet nozzle and the moving surface are spaced adistance that is between about 2-5 mm and greater than the size of thegap.
 20. A method as recited in claim 16 wherein the surface to becleaned is a peripheral surface of a roll, and wherein step (b) ispracticed by rotating the roll about an axis of rotation, and whereinstep (d) is practiced by linearly reciprocating the nozzle head in asubstantially horizontal direction subatantially parallel to the axis ofrotation of the roll.